Electrically powered mobile units such as cranes, trolleys, conveyors or the like, require considerable amounts of continuous uninterrupted current or power to function properly. Overhead electrical cranes for example, which are utilized extensively in heavy industries such as the basic steel industry, may be required to handle loads in excess of 300 tons. An interruption in the electrical power supply to such a crane while bridging (moving the crane along the runway), trolleying (moving the hoisting mechanism and load along the length of the crane), hoisting (raising the load), or while dynamic braking (motor braking), can result in damage to equipment and pose a threat to human life.
Generally, mobile units such as cranes obtain their power requirements from stationary electrified rails commonly referred to as "third rails". Such rails are usually mounted on the walls, floors, or beams of the structure, which supports the mobile unit, along the path which the mobile unit is intended to travel.
Examples of various means and methods of obtaining power for a mobile unit from an electrified rail or the like are disclosed by the following U.S. patents: Mayer U.S. Pat. No. 4,428,466, Weber U.S. Pat. No. 3,439,132, Kilburg U.S. Pat. No. 3,405,240, Maloney U.S. Pat. No. 3,397,291, Howell U.S. Pat. No. 3,303,294, Springings U.S. Pat. No. 3,124,226, Springings U.S. Pat. No. 3,114,441, Sierk U.S. Pat. No. 2,892,904, and Morris U.S. Pat. No. 2,210,684.
Unfortunately, many of these prior art methods exhibit disadvantages and drawbacks that make their use somewhat less than desirable. For example, some devices provide minimal surface contact between the electrified rail and the collector shoe. In many manufacturing environments wherein the atmosphere is laden with contaminating dirt and oils, such contaminents collect upon the surfaces of the rail contributing to excessive arcing which results in power interruptions and poor shoe life. To avoid the accumulation of contaminents on rails and the resultant effect thereof, a collector device must wipe the surface of the rail. Unfortunately, many prior art devices provide a degree of wiping which is wholly insufficient to keep the rails clean and avoid arcing. Also, many prior art devices create power interruptions because they are unable to adapt to the uneven contours or the misalignment of electrified rails. Furthermore, with many prior art devices in order to service or replace the conductive shoe, the entire collector shoe assembly must be disassembled or removed from the mobile unit resulting in excessive downtime and replacement and maintenance costs.